Noises induce complains and troubles most frequently among various pollutions, and prevention of noise as a countermeasure against an environmental problem is an important social subject.
Generally, there are two kinds of members of a sound insulation member and a sound absorbing member as sound-proof members for preventing noise.
The sound insulation member functions to cut the propagation of sound energy by reflecting a sound propagated in air, and the sound transmission loss, which is an index of the sound insulation property, basically depends on mass low, and becomes greater as the mass becomes greater. For example, mainly a concrete sound-proof panel or a metal sound-proof panel, such as those disclosed in, for example, JP-A-8-144227, is installed on a lowland portion or a high-level portion of a railway or a road for the purpose of reducing noise to inhabitants in the regions along the railway or road, as known well.
Since such panels made of these materials are heavy, although they have certain effects for preventing or diffusing noise generated from trains or cars depending on mass low, in a case of a metal sound-proof panel, there is a problem in durability such as deterioration, and in a case of a concrete sound-proof panel, recently there is a problem of flaking of small concrete pieces due to bulging or cracking caused by caustic embrittlement or rust of reinforcing steel. In particular, in a case of sound-proof walls made of concrete blocks, damage to the walls such as cracks and gaps is severe, and in a case where the installation place is at a high level such as a high-level bridge of a railway, flaking thereof becomes a problem, and therefore, urgent exchange is considered to be necessary.
Further, because the walls in both cases are great in specific gravity and heavy (for example, about 200 to 300 kg/m as a weight per unit length in the horizontal direction in an installation place), it is necessary to introduce heavy machines and an exclusive machine for attachment into an attachment place for conveying and attaching the walls. Especially, in a case where the installation place is a high-level bridge of railway, there remain a problem that it is difficult to approach the exclusive construction machine to the installation place of sound-proof walls from the railway line side, and a problem in workability because, even if the approach becomes possible, the work for installation inevitably becomes a high-level place working from a position under the high-level bridge.
For such problems, sound-proof panels made of FRP containing light-weight cores for the purpose of lightening are disclosed in JP-B-2-57691 and JP-A-9-170292. In these publications, because the use of sound-proof panels are limited mainly to outer walls of houses and buildings, the sound-proof panels disclosed in these publications are designed for a case where a noise source is relatively far, and they are not so high in sound insulation property. Further, small beams for attachment of the panels are provided in the lengthwise and crosswise directions at a fine pitch, and they are constructed as those which do not require high mechanical properties such as strength and stiffness so much.
However, in order to use the sound-proof panels as those for railways or roads, because noise sources are relatively close and the noise levels are high, it is necessary to control their weights at proper weights based on mass low. At the same time, it is preferred to sustain a panel by itself without providing small beams at a fine pitch, and because a wind pressure is applied, it is necessary to bear a wind pressure in the range of about 300 kg/m2 to about 400 kg/m2 per unit area. Namely, a light-weight sound-proof panel cannot be obtained unless an optimum design is performed with respect to sound insulation property and strength while an attachment means to a construction body such as a high-level bridge, a bridge or an edge of a road is considered. Further, in a case where the installation place is a high-level bridge such as a high-level bridge of railway, the panel itself may become a great noise source unless a resonance due to a vibration propagated from the construction body when a train is running is avoided.
Further, recently, for a sound-proof panel applied to a railway or a road, sound-proof countermeasures for houses or educational institutions adjacent to the railway or the road are further required, and the height of the sound-proof panel tends to become higher in order to also suppress a diffracted sound. However, the present construction body or beam has a weight limitation ascribed to the viewpoint of strength, and the height of the panel cannot be increased to a height more than a certain level. Further, although a light sound-proof panel made of acrylic is employed in consideration of such a weight limitation, there are a problem of durability due to a strength reduction ascribed to a deterioration by ultraviolet ray in a relatively short period, and a problem that the construction cost is not always cheep as a whole, because the strength and the stiffness are small and it is necessary to provide support poles and cross beams at a small interval though the sound-proof panel itself is light.
On the other hand, since the aforementioned sound absorbing member functions to damp a sound pressure by transforming a sound energy into a thermal energy, the sound absorbing member by itself is low in sound insulation property, and therefore, it is a general use to use it together with a sound insulation member, thereby increasing the sound insulation property. The invention using such a sound absorbing member and increasing the sound insulation property is disclosed in, for example, JP-A-2000-8331.
That invention disclosed is a sound-proof panel having a structure in which the sound insulation portion comprises a concrete sound insulation wall, therebehind an FRP sound absorbing plates are disposed at a predetermined interval, and an air layer is provided therebetween. Although this panel appears to be excellent in sound insulation property, because the sound insulation panel itself is made of concrete, there is still a problem of the aforementioned partial flaking or dropping of small pieces due to caustic embrittlement or temporal deterioration. Although it is tried to cover concrete with glass fiber reinforced plastic and prevent the flaking, it has not yet reached an essential improvement. Further, in a case of new installation, because the panels are made of concrete, heavy machines are required similarly to in the cases aforementioned.
It could therefore be advantageous to provide a sound-proof wall panel made of FRP and a sound-proof wall using this panel which have an effect for preventing a noise or diffusing or absorbing the noise, and do not cause flaking of small pieces due to deterioration thereof as in the conventional sound-proof walls made of concrete, which are light and excellent in handling property, and which can be installed easily even if the installation place is a high-level place, and a method for producing the same.